Heretofore, the normal manner for easily removing indicia from a substrate was to utilize a blackboard and chalk. The chalk is easily removed from the blackboard by any dry eraser. This system has many disadvantages, not the least of which is the fact that blackboards are relatively heavy and chalk is a messy and inconvenient substance to work with. Also, when writing on the blackboard and erasing the chalk material from the blackboard a fine dust is formed (from the chalk particles) which gets onto the floor, the hands of the person writing or erasing, and the clothes of such person. Moreover, chalk material is very inconvenient to carry because of the dusting problem and therefore is not normally readily available in homes and offices.
In view of the many disadvantages of using a blackboard-chalk system, it is readily apparent that it would be highly advantageous if an erasing system could be developed utilizing a readily available writing implement, such as a porous point pen, having an ink which can write on a smooth, hard surface such as a plastic and which would be easily erasable therefrom utilizing a dry erasing material such as a cloth or tissue paper. However, writing instruments employing a porous tip (such as a tip made of fibers suitably bonded together to provide a multiplicity of channels) and an ink reservoir require an ink which is readily uniformly fed to the tip from the reservoir, will not adversely effect the tip, will not dry out on the tip when the tip is exposed to atmospheric conditions for an extended period of time, and which does not have an objectionable odor. Many marking pens in current use utilize an aqueous ink because, inter alia, such inks generally do not have the objectionable odor of marking pen inks made with an aromatic solvent. However, such aqueous inks will, in general, not write on smooth, hard surfaces such as plastic because the inks will retract into small individual droplets. Additionally, such inks are not satisfactory for an erasing system because they are not easily erased after drying and will not write satisfactorily on a plastic substrate having sebum (a fatty oil-like material secreted by the sebaceous glands of the skin). Sebum on the writing substrate of a marking board is inevitable inasmuch as the writing substrate is extensively touched by the fingers. Hence, most porous point pen inks in use today are not satisfactory for use in an erasing system in which a plastic substrate is used as the writing surface and a dry eraser is utilized as the means for wiping the ink off of the plastic surface.